To observe a transparent specimen such as cells in a culture container, the phase contrast observation (refer to Non-patent Documents 1 and 2, for example) which can visualize its refractive index distribution is used suitably. To observe a transparent specimen which cannot be observed with naked eyes, a microscope or some other optical system is necessary even if the observation is intended to check the entire specimen roughly.    NON-patent Document 1: Hiroshi Komatsu, “Fundamentals and Application of Optical Microscopy (3),” Applied Physics, Vol. 60, No. 10, pp. 1,032-1,034, 1991    NON-patent Document 2: Hiroshi Komatsu, “ Fundamentals and Application of Optical Microscopy (4),” Applied Physics, Vol. 60, No. 11, pp. 1,136-1,138, 1991